Late Morning Models...Most Snow As the Storm Departs?

The morning computer model runs from 12z are now in. Here is the breakdown.

12z NAM: Precipitation will impact Southern New Jersey about 60 hours from now. The “540 Line” is above Cape May County and along Cumberland and Atlantic Counties. So there would be rain or some mixing in Atlantic City and Cape May and snow above that line. At hour 66, there is nothing but light snow on this model for the southern half of the state. However, a secondary plume of moisture seems to develop around Baltimore and Washington and by hour 72 this would clip Southeastern New Jersey. The “540 Line” pushes well off the coast so this would result in a light accumulation of snow if this model were to be believed. The storm is all offshore by hour 78.

12z GFS: Precipitation arrives by hour 54. The “540 Line” quickly rises into Northwestern New Jersey and Eastern Pennsylvania. This means rain is likely, perhaps initially mixing with sleet, for much of Central and Southern New Jersey. There could be some initial cold air leftover at the surface allowing for some freezing rain. Whether this gets prolonged is the big question on this model run. By hour 60 the storm intensifies offshore. A notable shift eastward in the “540 Line” is noted here, but it does not shift east enough by hour 60 to give the state a change back to wet snow. By hour 66, it does shift east and the GFS from 12z gives New Jersey heavy precipitation with the heaviest in Central and Southern New Jersey. The line shifts well offshore as the storm pulls away. The model would give the entire portion of Central and Southern New Jersey a pretty decent snowfall as the system pulls away, although some sleet could occur as well. The model shows portions of the state having 0.75 to 1.00 of liquid to work with which under normal circumstances would be 9 to 12 inches of snow without sleet. My guess would be (if this model is correct) that some of the snow would initially melt into the big puddles, but that a flash freeze would occur.

It is worth noting how both models changeover whatever precipitation we have in our region to wet snow as the storm is in the final six hours. My current feeling is that the NAM model is too dry. I think an overall trend will develop where interior sections have a very brief period of snow or wintry mix. The warmer air would then change the sleet or wet snow to rain. Then we have to see whether the surface is warm enough for plain rain or if there is going to be a corridor of freezing rain. After the change to rain, the ending of the storm would appear to bring the best chance for accumulating wet snow and sleet to Central and Southern New Jersey. This could end up being a four to six hour period of accumulating snow and flash freezing conditions. However, I caution this scenario has not always played out and is not normal for a storm in New Jersey. If you are traveling to Northwestern New Jersey, it appears as though it would be snow to a wintry mix and then back to snow.

I would also note that the 06z NAM run was more in line with the GFS from both 06z and 12z, although the 06z NAM was colder.